NAME¶
Pod::Usage, pod2usage() - print a usage message from embedded pod documentation
SYNOPSIS¶
use Pod::Usage
my $message_text = "This text precedes the usage message.";
my $exit_status = 2; ## The exit status to use
my $verbose_level = 0; ## The verbose level to use
my $filehandle = \*STDERR; ## The filehandle to write to
pod2usage($message_text);
pod2usage($exit_status);
pod2usage( { -message => $message_text ,
-exitval => $exit_status ,
-verbose => $verbose_level,
-output => $filehandle } );
pod2usage( -msg => $message_text ,
-exitval => $exit_status ,
-verbose => $verbose_level,
-output => $filehandle );
pod2usage( -verbose => 2,
-noperldoc => 1 )
ARGUMENTS¶
pod2usage should be given either a single argument, or a list of
arguments corresponding to an associative array (a "hash"). When a
single argument is given, it should correspond to exactly one of the
following:
- •
- A string containing the text of a message to print
before printing the usage message
- •
- A numeric value corresponding to the desired exit
status
- •
- A reference to a hash
If more than one argument is given then the entire argument list is assumed to
be a hash. If a hash is supplied (either as a reference or as a list) it
should contain one or more elements with the following keys:
- "-message"
- "-msg"
- The text of a message to print immediately prior to
printing the program's usage message.
- "-exitval"
- The desired exit status to pass to the
exit() function. This should be an integer,
or else the string "NOEXIT" to indicate that control should
simply be returned without terminating the invoking process.
- "-verbose"
- The desired level of "verboseness" to use when
printing the usage message. If the corresponding value is 0, then only the
"SYNOPSIS" section of the pod documentation is printed. If the
corresponding value is 1, then the "SYNOPSIS" section, along
with any section entitled "OPTIONS", "ARGUMENTS", or
"OPTIONS AND ARGUMENTS" is printed. If the corresponding value
is 2 or more then the entire manpage is printed.
The special verbosity level 99 requires to also specify the -sections
parameter; then these sections are extracted (see Pod::Select) and
printed.
- "-sections"
- A string representing a selection list for sections to be
printed when -verbose is set to 99, e.g.
"NAME|SYNOPSIS|DESCRIPTION|VERSION".
Alternatively, an array reference of section specifications can be used:
pod2usage(-verbose => 99,
-sections => [ qw(fred fred/subsection) ] );
- "-output"
- A reference to a filehandle, or the pathname of a file to
which the usage message should be written. The default is
"\*STDERR" unless the exit value is less than 2 (in which case
the default is "\*STDOUT").
- "-input"
- A reference to a filehandle, or the pathname of a file from
which the invoking script's pod documentation should be read. It defaults
to the file indicated by $0 ($PROGRAM_NAME for users of
English.pm).
If you are calling pod2usage() from a module and
want to display that module's POD, you can use this:
use Pod::Find qw(pod_where);
pod2usage( -input => pod_where({-inc => 1}, __PACKAGE__) );
- "-pathlist"
- A list of directory paths. If the input file does not
exist, then it will be searched for in the given directory list (in the
order the directories appear in the list). It defaults to the list of
directories implied by $ENV{PATH}. The list may be specified either by a
reference to an array, or by a string of directory paths which use the
same path separator as $ENV{PATH} on your system (e.g., ":" for
Unix, ";" for MSWin32 and DOS).
- "-noperldoc"
- By default, Pod::Usage will call perldoc when -verbose
>= 2 is specified. This does not work well e.g. if the script was
packed with PAR. The -noperldoc option suppresses the external call to
perldoc and uses the simple text formatter (Pod::Text) to output the
POD.
DESCRIPTION¶
pod2usage will print a usage message for the invoking script (using its
embedded pod documentation) and then exit the script with the desired exit
status. The usage message printed may have any one of three levels of
"verboseness": If the verbose level is 0, then only a synopsis is
printed. If the verbose level is 1, then the synopsis is printed along with a
description (if present) of the command line options and arguments. If the
verbose level is 2, then the entire manual page is printed.
Unless they are explicitly specified, the default values for the exit status,
verbose level, and output stream to use are determined as follows:
- •
- If neither the exit status nor the verbose level is
specified, then the default is to use an exit status of 2 with a verbose
level of 0.
- •
- If an exit status is specified but the verbose level
is not, then the verbose level will default to 1 if the exit status
is less than 2 and will default to 0 otherwise.
- •
- If an exit status is not specified but verbose level
is given, then the exit status will default to 2 if the verbose
level is 0 and will default to 1 otherwise.
- •
- If the exit status used is less than 2, then output is
printed on "STDOUT". Otherwise output is printed on
"STDERR".
Although the above may seem a bit confusing at first, it generally does
"the right thing" in most situations. This determination of the
default values to use is based upon the following typical Unix conventions:
- •
- An exit status of 0 implies "success". For
example, diff(1) exits with a status of 0 if
the two files have the same contents.
- •
- An exit status of 1 implies possibly abnormal, but
non-defective, program termination. For example,
grep(1) exits with a status of 1 if it did
not find a matching line for the given regular expression.
- •
- An exit status of 2 or more implies a fatal error. For
example, ls(1) exits with a status of 2 if you
specify an illegal (unknown) option on the command line.
- •
- Usage messages issued as a result of bad command-line
syntax should go to "STDERR". However, usage messages issued due
to an explicit request to print usage (like specifying -help on the
command line) should go to "STDOUT", just in case the user wants
to pipe the output to a pager (such as
more(1)).
- •
- If program usage has been explicitly requested by the user,
it is often desirable to exit with a status of 1 (as opposed to 0) after
issuing the user-requested usage message. It is also desirable to give a
more verbose description of program usage in this case.
pod2usage doesn't force the above conventions upon you, but it will use
them by default if you don't expressly tell it to do otherwise. The ability of
pod2usage() to accept a single number or a string
makes it convenient to use as an innocent looking error message handling
function:
use Pod::Usage;
use Getopt::Long;
## Parse options
GetOptions("help", "man", "flag1") || pod2usage(2);
pod2usage(1) if ($opt_help);
pod2usage(-verbose => 2) if ($opt_man);
## Check for too many filenames
pod2usage("$0: Too many files given.\n") if (@ARGV > 1);
Some user's however may feel that the above "economy of expression" is
not particularly readable nor consistent and may instead choose to do
something more like the following:
use Pod::Usage;
use Getopt::Long;
## Parse options
GetOptions("help", "man", "flag1") || pod2usage(-verbose => 0);
pod2usage(-verbose => 1) if ($opt_help);
pod2usage(-verbose => 2) if ($opt_man);
## Check for too many filenames
pod2usage(-verbose => 2, -message => "$0: Too many files given.\n")
if (@ARGV > 1);
As with all things in Perl,
there's more than one way to do it, and
pod2usage() adheres to this philosophy. If you
are interested in seeing a number of different ways to invoke
pod2usage
(although by no means exhaustive), please refer to "EXAMPLES".
EXAMPLES¶
Each of the following invocations of "pod2usage()" will print just the
"SYNOPSIS" section to "STDERR" and will exit with a status
of 2:
pod2usage();
pod2usage(2);
pod2usage(-verbose => 0);
pod2usage(-exitval => 2);
pod2usage({-exitval => 2, -output => \*STDERR});
pod2usage({-verbose => 0, -output => \*STDERR});
pod2usage(-exitval => 2, -verbose => 0);
pod2usage(-exitval => 2, -verbose => 0, -output => \*STDERR);
Each of the following invocations of "pod2usage()" will print a
message of "Syntax error." (followed by a newline) to
"STDERR", immediately followed by just the "SYNOPSIS"
section (also printed to "STDERR") and will exit with a status of 2:
pod2usage("Syntax error.");
pod2usage(-message => "Syntax error.", -verbose => 0);
pod2usage(-msg => "Syntax error.", -exitval => 2);
pod2usage({-msg => "Syntax error.", -exitval => 2, -output => \*STDERR});
pod2usage({-msg => "Syntax error.", -verbose => 0, -output => \*STDERR});
pod2usage(-msg => "Syntax error.", -exitval => 2, -verbose => 0);
pod2usage(-message => "Syntax error.",
-exitval => 2,
-verbose => 0,
-output => \*STDERR);
Each of the following invocations of "pod2usage()" will print the
"SYNOPSIS" section and any "OPTIONS" and/or
"ARGUMENTS" sections to "STDOUT" and will exit with a
status of 1:
pod2usage(1);
pod2usage(-verbose => 1);
pod2usage(-exitval => 1);
pod2usage({-exitval => 1, -output => \*STDOUT});
pod2usage({-verbose => 1, -output => \*STDOUT});
pod2usage(-exitval => 1, -verbose => 1);
pod2usage(-exitval => 1, -verbose => 1, -output => \*STDOUT});
Each of the following invocations of "pod2usage()" will print the
entire manual page to "STDOUT" and will exit with a status of 1:
pod2usage(-verbose => 2);
pod2usage({-verbose => 2, -output => \*STDOUT});
pod2usage(-exitval => 1, -verbose => 2);
pod2usage({-exitval => 1, -verbose => 2, -output => \*STDOUT});
Recommended Use¶
Most scripts should print some type of usage message to "STDERR" when
a command line syntax error is detected. They should also provide an option
(usually "-H" or "-help") to print a (possibly more
verbose) usage message to "STDOUT". Some scripts may even wish to go
so far as to provide a means of printing their complete documentation to
"STDOUT" (perhaps by allowing a "-man" option). The
following complete example uses
Pod::Usage in combination with
Getopt::Long to do all of these things:
use Getopt::Long;
use Pod::Usage;
my $man = 0;
my $help = 0;
## Parse options and print usage if there is a syntax error,
## or if usage was explicitly requested.
GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
pod2usage(1) if $help;
pod2usage(-verbose => 2) if $man;
## If no arguments were given, then allow STDIN to be used only
## if it's not connected to a terminal (otherwise print usage)
pod2usage("$0: No files given.") if ((@ARGV == 0) && (-t STDIN));
__END__
=head1 NAME
sample - Using GetOpt::Long and Pod::Usage
=head1 SYNOPSIS
sample [options] [file ...]
Options:
-help brief help message
-man full documentation
=head1 OPTIONS
=over 8
=item B<-help>
Print a brief help message and exits.
=item B<-man>
Prints the manual page and exits.
=back
=head1 DESCRIPTION
B<This program> will read the given input file(s) and do something
useful with the contents thereof.
=cut
CAVEATS¶
By default,
pod2usage() will use $0 as the path to
the pod input file. Unfortunately, not all systems on which Perl runs will set
$0 properly (although if $0 isn't found,
pod2usage() will search $ENV{PATH} or else the
list specified by the "-pathlist" option). If this is the case for
your system, you may need to explicitly specify the path to the pod docs for
the invoking script using something similar to the following:
pod2usage(-exitval => 2, -input => "/path/to/your/pod/docs");
In the pathological case that a script is called via a relative path
and
the script itself changes the current working directory (see "chdir"
in perlfunc)
before calling pod2usage, Pod::Usage will fail even on
robust platforms. Don't do that.
AUTHOR¶
Please report bugs using <
http://rt.cpan.org>.
Marek Rouchal <marekr@cpan.org>
Brad Appleton <bradapp@enteract.com>
Based on code for
Pod::Text::pod2text() written by
Tom Christiansen <tchrist@mox.perl.com>
ACKNOWLEDGMENTS¶
Steven McDougall <swmcd@world.std.com> for his help and patience with
re-writing this manpage.
SEE ALSO¶
Pod::Parser, Getopt::Long, Pod::Find